Chemical process

ABSTRACT

There is disclosed an improved process for preparing 1-hydroxy-3-oxa-1,2,4,5-pentane tetracarboxylic acid and 3,6-dioxa-1,2,4,5,7,8-octane hexacarboxylic acid wherein the unreacted starting acids are recovered in more desirable crystal habit. The acids are precipitated in salt form by lowering the pH of the reaction product to a range of from 4 to below 6 stepwise. The pH is lowered to above 6 in the first step and then relatively rapidly reduced to the desired level in the second step.

This invention relates to a process for making ether carboxylic acidsand more particularly to processes for making ether carboxylatesprepared by a calcium ion catalyzed reaction in alkaline medium ofmaleic acid salt and a carboxylate salt containing a reactive hydroxylgroup. Such reactions are of the type typically referred to as Michaelcondensation reactions.

Polycarboxylic acids have long been known to be useful, usually in thesalt form, as detergent builders or sequestrants. Also, ethercarboxylates useful as metal sequestering and detergent builders havebeen known and are most desirable for their beneficial effects inlaundering applications.

While many carboxylate compounds in the prior art have utility as abuilder or sequesterant in laundry detergent formulations, it has beenfound that certain ether carboxylates are more attractive and costeffective for such utility. In the field of detergent builders andsequesterants for laundry detergent formulations low cost of thecomponents is extremely important because it is in a very competitivemarket. While many ether carboxylate compounds have been found to beuseful there is needed more economical manufacturing processes wherebysuch compounds can be economically produced in large volume.

One example of ether carboxylates is a mixture of polycarboxylic acidsor salts thereof, particularly the sodium salts, of1-hydroxy-3-oxa-1,2,4,5-pentane tetracarboxylic acid (HOPTC) and3,6-dioxa-1,2,4,5,7,8-octane hexacarboxylic acid (DOOHC) which is highlyuseful in detergent formulations as a sequesterant or builder. Thismixture is prepared by reaction of a combination of D,L-tartrate saltswith maleate salts catalyzed by calcium ions. Due to equilibria presentin the reaction and to the need for the presence of particular reactantratios to obtain particularly preferred ratios of HOPTC and DOOHC in theproduct, there is considerable unreacted D,L-tartrate and maleatepresent at the end of the condensation reaction. Further, to provide amore economical process it is desired that a means be found toeconomically recover and reuse the unreacted D,L-tartrate and maleaterather than merely discharging maleate and tartrate as waste.

SUMMARY OF THE INVENTION

In accordance with this invention, there is provided a process forpreparing HOPTC and DOOHC by the reaction of the salts of maleic acidand a tartaric acid said reaction catalyzed by calcium ions andconducted under alkaline conditions wherein unreacted salts areconveniently recovered in such manner that they may be recycled to thesynthesis reaction to produce additional HOPTC and DOOHC. It has beendiscovered that at a limited range of acidity certain unreacted saltsare conveniently recovered from the reaction mixture at the conclusionof the reaction. By reducing the pH of the reaction mixture to a rangewithin about 4.5 to about 5.5 by combining a suitable acid with thereaction mixture, the insoluble salts of starting acids precipitatewhile the desired ether carboxylate product remains in solution. Theprecipitate is removed by known means such as filtration therebyallowing further processing of the ether carboxylate solution.

A process whereby precipitate is produced by stepwise reduction of pHhas been discovered wherein the precipitate is provided in improvedform. That is, the pH of the crude reaction mixture is reduced to withina range of from about 6.0 to about 9 in the first step and then the pHof the reaction mixture is reduced to the desired range of from about4.5 to about 5.5 relatively more rapid. It has been found that by theprocess of this invention the precipitate produced is of sufficientporosity to allow much faster filtration rates and provides a filtercake having less residual free liquid. Because the filter cake containsless free liquid it can be transported more efficiently.

In another aspect of this invention, the calcium ions employed tocatalyze the condensation reaction to prepare the ether carboxylate isconveniently recovered and recycled to the synthesis reaction byprecipitating the calcium as a calcium carbonate. The precipitation isaccomplished by combining the reaction mixture, typically after removalof unreacted starting salts, with an alkaline earth or alkali metalcarbonate at a pH in the range of from about 7 to about 12. Theprecipitate is removed by known means, preferably by filtration.

DETAILED DESCRIPTION OF THE INVENTION

Calcium catalyzed reactions for the production of ether carboxylates areknown. A typical example of such a process is disclosed in U.S. Pat. No.4,663,071 to Bush et al and such patent is hereby incorporated byreference.

The U.S. Patent discloses a process for preparing a mixture of HOPTC andDOOHC referred to above. In such process the mixture is obtained by thereaction of maleic acid and tartaric acid salts. This disclosure is atypical example of the reaction of maleic acid with tartaric acid saidreaction being catalyzed by calcium ions and conducted in alkalinemedium. Such reactions are known in the art as Michael condensationreactions. It is typical of the Michael condensation reactions toprovide the most effective equilibrium state for the production of thedesired compound or mixture by control of the reactant ratio.

It has been found that D,L-tartaric acid salts possess differentsolubility characteristics than do either the D- or L- isomers such thatthe D,L- isomer conveniently precipitate from solution at a pH in therange of from about 7 to about 9.5 while the calcium salts of HOPTC andDOOHC remain in solution and can be purified for use as a buildercombination in detergent formulations.

The recovery of unreacted maleate salts from calcium catalyzed reactionsof maleic acid salts with salt of tartrate salts in alkaline medium isconveniently achieved by acidifying the reaction product so as to reducethe pH to within the range of about 4 to below about 6.

A particular advantage of the process of this invention, wherebyunreacted maleate salt is recovered, is the ability to regulate thereactant ratio more freely since convenient recovery and recycle ispossible. Loss of unreacted maleate salt is insignificant and itsrecovery economical, particularly when maleic acid is employed to reducethe pH of the reaction product of the condensation reaction.

In accordance with one embodiment of this invention the unreactedD,L-tartrate and maleate starting materials are removed by precipitationfrom the reaction mass prior to the removal of calcium from the system.Specifically, calcium D,L-tartrate and mono sodium maleate areprecipitated from the reaction mixture by adjustment of the pH of thereaction solution in two steps. The precipitate of calcium D,L-tartrateand mono sodium maleate is then returned to a subsequent condensationsynthesis reaction. It has been found that the small amounts ofby-products such as malate and fumarate and residual amounts of HOPTCand DOOHC trapped in the precipitate are not deleterious to the use ofthis recycled precipitate in subsequent condensation synthesis reaction.

FORMATION OF HOPTC/DOOHC MIXTURES

The first step is the synthesis of HOPTC/DOOHC mixtures by the reactionin aqueous medium of maleate and D,L-tartrate reactants comprising bothmonovalent cation and calcium salts of maleic acid and D,L-Tartaricacid. As noted above, the total amount of maleate plus D,L-tartratereactants in the aqueous reaction mixture will generally range fromabout 20% to about 70% by weight of the mixture, more preferably fromabout 55% to about 65% by weight. Calcium maleate is provided by firstreacting maleic acid with calcium hydroxide or calcium carbonate thelater preferably provided at least in part by recycle from earlierreactions. The D,L-tartrate is provided by hydroxylation of maleic acid(from maleic anhydride) in the presence of a catalyst and hydrogenperoxide by known means. One portion of the D,L-tartaric acid employedin the synthesis reaction is taken from the neutralized hydroxylationreaction product. Another portion of the needed D,L-tartrate is providedby the recycled calcium D,L-tartrate provided by earlier reactions aswill be more fully described below.

The molar ratio of maleic acid to D,L-tartaric acid in the reactionmixture provided from all the sources noted above will generally rangefrom about 0.5:1 to 8:1, more preferably from about 0.8:1 to about1.2:1. The ratio of reactants will control the ratio of HOPTC/DOOHC inthe final product.

As noted above the synthesis reaction takes place in the presence of acatalyst comprising calcium ions. To provide the necessary amount ofcalcium cation, several sources are used. Calcium maleate, prepared fromrecycled calcium carbonate and maleic acid provides one calcium ionsource. Previously used but unreacted calcium D,L-tartrate recovered inthe process of this invention provides another major calcium ion source.Any additional needed calcium ions usually a very small amount, can beprovided by an additional calcium ion source such as calcium hydroxideadded either as a solid or as a slurry. Other water soluble calciumsalts can be employed, but calcium hydroxide possesses the additionaladvantage of supplying needed hydroxide ions. The total amount ofcalcium ion present provides a total molar ratio of calcium cation tomaleate of 1:1. However, the amount of calcium cation can vary greatlyand may be such that the ratio of moles of calcium cations to totalmoles of maleic and D,L-tartaric acids in solution can approach, but beless than 1.

The hydroxide of a monovalent cation is also essentially added to thereaction mixture as a source of alkalinity. This neutralizing agent isusually added in an amount such that the ratio of moles of monovalentcations to total moles of D,L-tartaric acid plus the moles of maleicacid minus the moles of calcium cations ranges from about 2.1:1 to about3.8:1 More preferably this ratio ranges from about 2.2:1 to about 3.3:1.The monovalent cation-containing neutralizing agent can be any hydroxidewhich upon addition to water yields monovalent neutralizing cations insolution. Such neutralizing agents include, for example, alkali metal,ammonium or substituted ammonium hydroxide. Sodium hydroxide is highlypreferred.

Sufficient neutralizing agent which, in combination with calciumhydroxide, is added to the synthesis reaction mixture to insure that thereaction mixture is over-neutralized. Thus, the reaction mixture in theprocess of this invention will generally have a pH within the range offrom about 8.5 to 13, more preferably from about 10.5 to about 12.5. Theaqueous reaction mixture, after the appropriate amounts of reactants,catalysts and neutralizing agent are combined, is maintained at atemperature of from about 20° C. to about 120° C., preferably from about70° C. to about 95° C. for a period of time sufficient to form areaction product mixture containing the desired amounts of HOPTC andDOOHC. Reaction times of from about 0.5 to 50 hours, more preferablyfrom about 1 to 4 hours, would generally be suitable for realizingacceptable yields of the 2 components of the desired mixture Reactiontime is highly affected by temperature whereby higher temperatureincreases the rate of reaction.

At completion of the reaction the mixture is quenched with water to coolit to a temperature in the range of 80° C. Addition of water alsoimproves the handling of the viscous reaction mass.

MONOSODIUM MALEATE AND D,L-TARTRATE PRECIPITATION

The reaction mixture containing mixed salts of HOPTC and DOOHC alsocontains relatively large amounts of unreacted maleic and tartrate acidsalt. These salts are recovered and recycled to provide higherefficiency of utilization of this valuable raw material.

The recovery of these salts is achieved by a two step method of loweringof the pH of the reaction mixture whereby sodium hydrogen maleate ormonosodium maleate and calcium tartrate precipitate. In the preferredembodiment the reaction mixture is cooled and diluted with water. Anacidic material such as sulfuric acid, or an organic acid such as formicacid is combined with the reaction mixture in sufficient amount to bringthe combined synthesis mass and acid to an initial pH in the range offrom about 6.0 to about 9, preferably slightly below 7. Then, withfurther addition of suitable acid the pH of the reaction mixture isrelatively more rapidly acidified further to a pH in the range of fromabout 4.5 to below 6, preferably to about 4.8 to about 5.2.

Any number of acidic materials can be employed to lower the pH of thereaction mixture. Combinations of acidic materials may also be employed.Typical examples of such acids are sulfuric acid, hydrochloric acid,nitric acid, formic, acetic, propionic, butyric and D,L-tartaric,carbonic, phosphoric, sulfonic, sulfurous, boric, phosphorous, adipic,benzoic, citric, fumaric, glycolic, malic, maleic, malonic, oxalic,succinic, sorbic, nitrilotriacetic, long chain fatty acids, etc.

In the process of this invention, the acid substance may be added to thecrude reaction mass. Alternately, the reaction mass may be added to aheel containing the acid substance. In a further process of thisinvention, the acid substance and the reaction mass may be addedconcurrently into a mixing vessel. Sufficient water is added to thereaction mass and/or acid material so that the final concentration ofdesired ether carboxylate in the completed mixture is about 40%.

Sufficient acid is added to reach a preferred pH of near 5.0 and theprecipitated reaction mass is cooled to below 50° C., preferably fromjust above the freezing point of the mixture to about 40° C. mostpractically to from about 20° C. to about 30° C. to obtain usablefiltration rates in large scale production. In a preferred mode, coolingthe reaction product from the 80° C. reaction temperature to 65° C. over30 minutes is followed by slow cooling to from about 30° C. to about 40°C. The suspension is then allowed to rest for about 30 minutes. Theslurry is preferably cooled slowly with mild or slow agitation so as togrow particles which can be filtered in an appropriately short time.Other methods of acid addition such as are noted above can also beemployed with appropriate adjustment of precipitation conditions.

In the process of this invention wherein HOPTC and DOOHC are produced ithas been found that both unreacted starting acids, D,L-tartaric acid andmaleic acid can be recovered in their salt form. Also, it has been foundthat the calcium salt of D,L-tartaric acid precipitates from thereaction mixture at a pH in the range of from about 7 to about 12 and istypically of smaller crystal habit than the maleate salt. However,according to this invention the two acid salts may be precipitated in atwo step procedure which produces globular particles including both acidsalts.

When a mixed acid solution is employed to precipitate tartrate andmaleate in the process of this invention, the acids may be added eithersequentially or concurrently. In one mode of operation, the reactionmass at a temperature of about 80° C., is added to a heel of aqueousacid, typically formic acid, and then a solution of maleic acid is addedto the partly neutralized reaction mass.

It has been found that when the pH of the reaction mixture is in theabove-stated range calcium D,L-tartrate precipitates when such mixtureis diluted with water or cooled to a temperature in the range of fromabout at least above freezing to about 70° C. The reaction mixture istypically diluted with water in amounts up to about 200 percent byweight. Greater dilution may be accomplished but additional amounts ofwater are not beneficial due to increased solubility or the salts beingprecipitated and also would probably require removal later. Dilution ofthe reaction mixture by about 30 to about 80 percent, by weight, istypical and usually both cooling and dilution are employed to providemaximum amount of tartrate precipitation.

In the process of this invention, there is employed, in conjunction withthe above-noted stepwise reduction of pH, the use of crystal seedingwhereby small particles of calcium tartrate/monosodium maleate recoveredfrom previous production of mixtures of HOPTC and DOOHC are added to thereaction mixture. Thus, when the temperature of the reaction mixture isfirst reduced to about 80° C. by diluting the reaction mixture as notedabove, crystals of calcium tartrate/sodium maleate from a previous batchare introduced into the reaction mixture. Amounts of crystals in therange of up to about 30 percent of the expected weight of the freshprecipitate may be added. When crystals are employed from the previousfilter cake there is provided seed crystals of monosodium maleate. Thesecrystals dissolve leaving calcium tartrate. However, the dissolvedmonosodium tartrate buffers the solution to a pH of about 6. When the pHis reduced in the second step dissolved monosodium maleate begins toprecipitate below about 5.8.

Following the addition of crystals, the pH of the reaction mixture isthen slowly reduced by combining the reaction mixture with acid toprovide a reaction mixture having a pH in the range of about 7 to about9 without prior seeding as described above. However, with seeding asnoted above it is more preferable to reduce the pH of the reactionmixture in the first step of pH reduction to from about 6 to about 7.While lowering the pH of the reaction mixture it is also cooled to atemperature in the range of from above the freezing point of the mixtureto about 50° C. It has been surprisingly found that, in the second stepof pH reduction when the pH of the reaction mixture is reduced rapidly,or over a brief period of time, for example up to about one minute toabout 10 minutes, unexpectedly large agglomerates of the combined saltsof calcium tartrate and monosodium maleate are created. Throughout pHreduction, cooling is required to maintain the temperature of thereaction mixture in the desired range of from above freezing to about35° C. As noted above, the reaction mixture is held for about 30 toabout 40 minutes after final pH reduction to allow crystal formation. Itis preferred to allow a short rest period between steps whereby thereaction mixture, at a pH above about 6, rests for about 10 minutesbefore the second step of pH reduction is performed. The largeragglomerates are more easily separated from the reaction mixture.

Removal of the precipitated acid salt may take any form practical andtypically is performed by continuously drawing the slurry from theprecipitator to a belt or drum filter or centrifuge. Other forms ofremoval such as decantation, etc. may also be employed. The filtratecontains the ether carboxylate in salt form. In a preferred embodimentthe filtrate is transferred to another precipitator for removal of thecalcium cations in the form of calcium carbonate.

In the production the HOPTC/DOOHC mixture filter cake is discharged and,in one embodiment, reslurried with water. The slurry is recycleddirectly or indirectly to the synthesis reactor to supply a portion ofthe required D,L-tartrate and maleate salts. Preferably the recoveredmaleate salt and/or D,L-tartrate salt is slurried with water and mixedwith calcium maleate for recycle into the synthesis reaction.

CALCIUM CARBONATE PRECIPITATION

After removal of the insoluble acid salt or salts as described above,the filtrate from such operation is recovered and purified for use asdetergent builder. In a preferred embodiment, calcium is removed eitherbatchwise or preferably continuously. Typically, the filtrate from theabove-mentioned step is pH adjusted with a base, preferably sodiumhydroxide, as it is being fed into a calcium carbonate precipitator tobring the pH of the solution into a range of from about 10 to about 12,preferably from about 10 to about 10.5. The pH adjustment may beperformed either in the precipitator or in a separate vessel if desired.The pH adjusted material is maintained in the range of from about 75° C.to about 110° C., preferably at about 90° C. to 100° C. Concurrently asolution of a basic carbonate, preferably sodium carbonate, preferablyat a concentration of about 25%, is added to the precipitator to providean overall mole ratio of carbonate to calcium of 1.3:1.

Alternatively, calcium carbonate is removed by increasing the mole ratioof carbonate ion to calcium ion without change in pH.

Although this invention is described with respect to carbonateprecipitation using the preferred sodium cation, it is to be understoodthat other suitable cations may also be employed to obtain precipitationof calcium carbonate. Other cations useful in the process of thisinvention include potassium, ammonium or organo substituted ammonium.Other salts may be employed to obtain the calcium carbonate precipitateand includes sodium bicarbonate and mixtures of carbonates andbicarbonates.

During the precipitation of calcium carbonate it is preferred that wateris continuously removed from the slurry to maintain the concentration ofthe organic acid salts in the range of from about 30% to about 50% byweight. Filtration of the precipitated calcium carbonate may take anyform practical and typically is performed by continuously drawing theslurry from the precipitator to a centrifuge or to a belt or drumfilter. The filtrate contains the desired ether carboxylate mostly asthe alkaline salt along with minor amounts of raw material andby-products. In the preparation of HOPTC/DOOHC mixtures, the by-productscomprise typically less than 20% by weight of the HOPTC and DOOHCpresent.

The wet cake from the separation is mechanically reslurried with waterto form an approximately 50% calcium carbonate slurry for recycle to thesynthesis reaction. The recovered carbonate may be added directly to theether carboxylate synthesis reactor or together with recovered,unreacted tartrate and maleate. Preferably, the recovered calciumcarbonate is converted to calcium maleate in a separate vessel beforereturn to the synthesis reaction.

CALCIUM MALEATE FORMATION

Before introduction into the synthesis reaction, the calcium carbonateprecipitate obtained from the product as described above is preferablyconverted to calcium maleate by reaction with maleic acid. Preferably,the maleic acid is prepared in situ. In one embodiment, the maleic acidis prepared by charging molten maleic anhydride to water heated to 65°C. to 75° C. After hydrolysis of the maleic anhydride to maleic acid iscomplete, the slurry of calcium carbonate solids is added at a rate slowenough to avoid uncontrolled foaming due to the evolution of carbondioxide. During the addition of calcium carbonate the reaction mass isheated to a temperature in the range of from about 90° C. to about 100°C. and preferably to about 95° C.

In the production of HOPTC and DOOHC it is preferred that calciumD,L-tartrate and monosodium maleate slurry obtained from thetartrate/maleate removal step is added to the calcium maleate whileheating to a boil at atmospheric pressure. The mixture is held atboiling for about 15 minutes to ensure conversion of all of the calciumcarbonate to the maleate. The mixture is then charged to the synthesisreactor for the preparation of additional HOPTC and DOOHC. Duringtransfer to the synthesis reactor water may be evaporated to reducevolume.

Although the above described process follows a particular scheme, it isobvious that other schemes or flow charts may also be followed. Forexample, hold tanks, mixing tanks and transfer tanks may be employedwhich are not described above. Other variations will occur to thoseknowledgeable in the art.

EXTRACTION

The filtrate obtained from the procedure to remove calcium carbonate ispurified by extraction with methanol and water. Such purification in theproduction of HOPTC and DOOHC mixtures is shown in U.S. Pat. No.4,633,071 referred to above.

According to such patent the solution obtained after removal of calciumcarbonate is thoroughly mixed with methanol. After settling, two layersform because the desired solution of HOPTC and DOOHC is less soluble inmethanol than the impurities to be removed. The undesired solution isdecanted and stripped of residual methanol. The residue is dissolved inwater and extracted again with methanol.

After purification the product is concentrated so as to provide thedesirable concentration of ether carboxylate solution for use asdetergent builder or sequestrant. The concentrated material may also bedried by any typical means such as by spray drying, etc. to providegranular or particulate material which is the form traditionallyemployed.

To further illustrate the process of the present invention there isdescribed below nonlimiting preferred embodiments. In the followingexamples all percentages are by weight unless otherwise noted.

EXAMPLE 1

Into a round bottom flask equipped with a thermometer, addition funnel,condenser and mechanical stirrer there were placed 39.4 g of maleicanhydride and 200 g of water. The mixture was heated to 70° C. to formmaleic acid to which was added 50.1 g of calcium carbonate. Then wetfilter cake, 350 g, from a previous run together with 100 g of waterwere added to the flask. The wet cake contained the following in weightpercent:

Disodium meso tartrate--0.321

Calcium D,L-tartrate--19.62

Disodium Malate--1.27

HOPTC--13.24

DOOHC--0.7

Monosodium Fumarate--15.71

After addition of wet cake 62.95 g of D,L-tartaric acid and 550 g ofdisodium tartrate solution obtained by hydrolysis of epoxysuccinate wereadded to the reaction. This mixture was heated to 90° C. with stirring.Air was swept through the reactor to remove about 760 g of water duringa period of 70 minutes after the reaction mass reached 90° C. Then 127.9g of sodium hydroxide, 50% solution, was added to the mixture. Heatingat 90° C. was continued for another 90 minutes. The reaction mixture wasquenched with 126 g of water to reduce the organic solids content from65% to 54% thereby cooling the reaction mass from 90° C. to about 80° C.The resulting mixture, a clear solution, was then divided into 2 partswith Portion A containing 566 g and Portion B containing 280 g.

A

Into this portion of the reaction mixture 40 g of filter cake from aprevious reaction containing both calcium tartrate and sodium hydrogenmaleate together with 160 g of water were added and the reaction massheld at 60° C. After holding for 10 minutes at that temperature formicacid was added over 20 minutes to lower the pH to 5.9. After reducingthe pH the reaction mixture was cooled to 35° C. over 30 minutes. Thereaction mixture was then held at 35° C. for an additional 30 minutes. Asample was taken for a filtration rate test (A-1). Then a 40% maleicacid solution was added to adjust the pH to 4.85 over a period of about5 minutes and the system again held at 35° C. for an additional 30minutes. Another sample was taken (A-2).

B

In this portion of the reaction mixture there were added 15 g of calciumtartrate filter cake as described above in Part A together with 80 g ofwater. The diluted reaction mixture was then cooled to 35° C. Thenformic acid was added over a period of 20 minutes to adjust the pH to 6.The reaction mixture at the lower pH value was held at 35° C. for 45minutes and a sample taken for a filtration rate test (B-1). A 40%maleic acid solution was added to adjust the pH to 4.8 with relativelyrapid addition and the system held at 35° C. for an additional 30minutes. Another sample was taken for a filtration rate test (B-2). Theresults of these tests are presented below in Table I. As shown in Table1, the filtration rates of both samples in Part B are much lower thanthe samples in Part A. This is believed to be due to the addition ofgreater amounts of crystal seed material from the previous filter cakein Part A. The filtration rate reported in Table I below was measured ata cake thickness of 12.7 mm.

                  TABLE I                                                         ______________________________________                                        Sample         A-1    A-2        B-1  B-2                                     ______________________________________                                        pH during filtration                                                                         5.9    4.85       6.0  4.8                                     Filtration rate                                                                              4237   11,407     1263 3259                                    liters/hr/meter.sup.2                                                         ______________________________________                                    

The filtrates were analyzed to determine their components. The resultsof the analyses are shown in Table II below. The results indicate thatthe maleate salt is mostly removed from the system at the lower pH eventhough maleic acid is employed to acidify the reaction mixture.

                  TABLE II                                                        ______________________________________                                        Analyses       A-1    A-2       B-1  B-2                                      ______________________________________                                        Disodium tartrate                                                                            2.2    1.9       2.0  1.6                                      Disodium malate                                                                              0.3    0.3       0.0  0.0                                      Disodium maleate                                                                             4.6    0.7       4.3  0.5                                      Disodium fumarate                                                                            1.1    1.2       1.1  1.0                                      HOPTC          21.0   21.5      20.4 20.0                                     DOOHC          3.2    3.3       3.1  3.3                                      ______________________________________                                    

EXAMPLE 2

This example demonstrates the disadvantage of cooling the reactionmixture before reducing the pH by combining their mixture with acid. Areaction mixture obtained in accordance with the procedure of Example 1was obtained and divided into four equal portions of 180 g, then eachwas quenched with 40 g of water. A heel comprising 10 g of formic acid,88%, and 40 g of water was prepared for each portion.

One portion of the reaction mixture at 52° C. was added to the acid heelthereby lowering the pH of the mixture to about 6.9 while coolingcontinued over a period of about 32 minutes. Cooling was then continueduntil the reaction mixture and the combined heel reached about 34° C.The maleic acid mixture, 40%, was then added over a period of about 5minutes with continued cooling to maintain the reaction mixture at about34° C. and lowering the pH to 5.0. Globular precipitate formed and themixture was then filtered to recover the precipitate.

B

The reaction mixture was cooled to 43° C. before being added to theheel. The combined heel and reaction mixture was further cooled to atemperature of about 30° C. during combination which produced a pH of7.05 after holding at the noted temperature and pH for about 10 minutes.Maleic acid was then added to the solution over a period of 6 minuteslowering the pH to 5.0. The resulting mixture was then filtered torecover the precipitate.

The filtration rate of each precipitate was measured during filtrationand the results appear in Table III below.

                  TABLE III                                                       ______________________________________                                                      Filtration Rate - liters/hr/M.sup.2                             Cake Thickness - mm                                                                           A          B                                                  ______________________________________                                         9.5            2770.3     1751.8                                             12.7            2077.7     1495.1                                             15.8            1670.7     1197.7                                             ______________________________________                                    

The data in Table III above indicates that combining the reactionmixture with the acid heel at higher temperature improves the filtrationrates.

EXAMPLE 3

A reaction mixture obtained in accordance with the procedure of Example1, 360 g, was quenched with 80 g of water and cooled to about 80° C. Anacid heel was prepared by combining 23 g of 88% formic acid and 80 g ofwater. Into this heel was charged the quenched reaction mixture;however, the pH was lowered, with cooling to about 35° C. as it wascombined with the acid heel in the one step whereby the pH of thecombination reached about 6.3. Maleic acid, 40%, was added over a periodof one hour resulting in a final pH of 5.0. Cooling continued for anadditional one hour and 40 minutes to obtain a final temperature of 32°C. The precipitate was recovered by filtration and the filtration ratesat the varying filter cake thicknesses are reported below.

                  TABLE IV                                                        ______________________________________                                        Cake Thickness - mm                                                                          Filtration Rate - liters/hr/M.sup.2                            ______________________________________                                         9.5            1222.2                                                        12.7           937                                                            15.8           774                                                            ______________________________________                                    

By comparing the data presented in Tables III and IV the improvement infiltration rate in accordance with this invention is clearly shown.

There has been described a novel process of general application for theproduction of ether carboxylates. While the process has been describedwith reference to specific compounds no intention is made by suchreference to limit the scope of this invention unless expressly stated.Various modifications may be made in the materials and sequence ofprocess steps as well as process combinations which are adapted to suitthe various reactants and products without departing from thisinvention.

I claim:
 1. In a process for preparing mixtures of1-hydroxy-3-oxa-1,2,4,5-pentane tetracarboxylic acid and3,6-dioxa-1,2,4,5,7,8-octane hexacarboxylic acid which comprisesreacting in an alkaline reaction medium the salts of maleic acid andtartaric acid in the presence of calcium ion catalyst, wherein the pH ofthe reaction product is reduced to a range of from about 4 to below 6,the improvement comprising reducing the pH in two steps wherein in thefirst step the pH is reduced to a pH of from about above 6 to about 9 andin the second step the pH is reduced at a more rapid rate than in saidfirst step whereby unreacted starting acids are precipitated inparticles of a size which provide increased porosity and filter rate,recovering said acids from the reaction product.
 2. The process of claim1 wherein the temperature of the reaction product is cooled to atemperature in the range of from above freezing to about 50° C. duringreduction in pH.
 3. The process of claim 1 wherein the second step of pHreduction is delayed for a period of about 10 minutes after completionof the first step.
 4. The process of claim 1 wherein the pH of thereaction product at the end of the first step is in the range of fromabout 6.0 to about 7.0.
 5. The process of claim 4 wherein the pH of thereaction product at the end of the second step of pH reduction is in therange of about 4.8 to about 5.2.
 6. The process of claim 1 wherein thepH is reduced in the first step by adding the reaction product to a heelcontaining acid.
 7. The process of claim 6 wherein the pH of thereaction product is reduced by addition of maleic acid.
 8. A process ofclaim 1 wherein the pH is reduced by combining the reaction product withan organic acid.
 9. A process of claim 8 wherein the organic acid isselected from the group consisting of formic, acetic, propionic, citric,maleic, tartaric, fumaric, malic, malonic, succinic, adipic, butyric andlong chain fatty acids.
 10. A process of claim 1 wherein the pH isreduced by combining the reaction product with an inorganic acid.
 11. Aprocess of claim 10 wherein the inorganic acid is selected from thegroup consisting of sulfuric, hydrochloric, carbonic, nitric,phosphoric, phosphorous, sulfonic and sulfurous acids.
 12. A process ofclaim 1 wherein the pH is reduced by combining the reaction product witha mixture of organic and inorganic acid.
 13. A process of claim 12wherein the acids are sulfuric and maleic acids.
 14. A process of claim12 wherein acid heel contains a mixture of two acids.
 15. A process ofclaim 14 wherein the acids in the heel are formic and maleic.
 16. Aprocess of claim 1 further including the step of reducing the amount ofcalcium in the reaction product after removal of the unreacted startingacids by means of increasing the pH of the remaining solution to withina range of from about 7 to about 12 and combining the reaction productwith a basic carbonate whereby calcium carbonate precipitates and isremoved from the reaction product.
 17. A process of claim 16 wherein thebasic carbonate is sodium carbonate.
 18. A process for preparing amixture of the alkali metal salt of 1-hydroxy-3-oxa-1,2,4,5-pentanetetracarboxylic acid and 3,6-dioxa-1,2,4,5,7,8-octane hexacarboxylicacid which comprises the steps of:(a) forming an aqueous reactionmixture comprising from about 20% to 60% by weight of both calcium andmonovalent cation salts of maleic acid and tartaric acid, said mixturecorresponding to the over-neutralized mixture which is formed bycombining:(i) maleic and tartaric acids in a maleic to tartaric molarratio of from about 0:5:1 to about 8:1; (ii) a source of calcium cationsin an amount such that the molar ratio of calcium to tartaric acidranges from about 0.1:1 to 2.0:1 with the ratio of moles of calcium tototal moles of maleic and tartaric acid being less than 1; and (iii) aneutralizing agent comprising a hydroxide of a monovalent cation in anamount such that the ratio of moles of monovalent cation to moles ofmaleic acid plus moles of tartaric acid minus moles of calcium rangesfrom about 2.1:1 to 3.8:1. (b) maintaining said aqueous reaction mixtureat a temperature of from about 20° C. to 120° C. for a time periodsufficient to form a reaction product mixture of said1-hydroxy-3-oxa-1,2,4,5-pentane tetracarboxylic acid salts and3,6-dioxa-1,2,4,5,7,8-octane hexacarboxylic acid salts; (c) lowering thepH of reaction mixture of step (b) to the range of from about 4.5 toabout 5.5 and cooling the mixture to precipitate calcium tartrate andmonosodium maleate in two steps wherein the pH is first reduced to arange of from about 6 to about 9 then lowering the pH more rapidly thanin said first step whereby unreacted starting acids are precipitated inparticles of a size which provides increased porosity and filter rate;(d) removing the precipitate from the reaction mixture formed in step(c) and recycling it to step (a) to prepare additional amounts ofreaction product; (e) treating the reaction mixture from step (d) with acarbonate or bicarbonate whereby calcium carbonate precipitates; (f)removing the calcium carbonate from the reaction mixture of step (e) andrecycling it to step (a) to prepare additional amounts of reactionproduct; and (g) recovering and purifying the reaction mixture from step(f).
 19. A process of claim 18 wherein the pH of the filtrate of step(d) is in the range of from 9 to 11 before combining with the carbonate.20. A process of claim 18 wherein the mole ratio of carbonate to calciumin step (d) is 1.3:1.0.
 21. A process of claim 18 wherein theneutralizing agent is sodium hydroxide.
 22. In a process for preparingmixtures of 1-hydroxy-3-oxa-1,2,4,5-pentane tetracarboxylic acid and3,6-dioxa-1,2,4,5,7,8-octane hexacarboxylic acid which comprisesreacting in an alkaline reaction medium the salts of maleic acid andtartaric acid in the presence of calcium ion catalyst, wherein the ph ofthe reaction product is reduced to a range of from about 4 to below 6the improvement comprising reducing the pH in two steps wherein in thefirst step the pH is reduced to a pH of from about 6 to about 9 an dinthe second step the pH is reduced at a more rapid rate than in saidfirst step whereby unreacted starting acids are precipitated inparticles of a size which provide increased porosity and filter rate,recovering said acids from the reaction product, then increasing the pHof the remainder of the reaction mixture by addition of a carbonate orbicarbonate whereby calcium carbonate precipitates and is removed fromthe reaction mixture and reacting said calcium carbonate with maleicacid to form a calcium salt of said acid for use in said process.
 23. Aprocess for preparing a mixture of the alkali metal salt of1-hydroxy-3-oxa-1,2,4,5-pentane tetracarboxylic acid and3,6-dioxa-1,2,4,5,7,8-octane hexacarboxylic acid which comprises thesteps of:(a) forming an aqueous reaction mixture comprising from about20% to 60% by weight of both calcium and monovalent cation salts ofmaleic acid and tartaric acid, said mixture corresponding to theover-neutralized mixture which is formed by combining:(i) maleic andtartaric acids in a maleic to tartaric molar ratio of from 0.5:1 toabout 8:1; (ii) a source of calcium cations in an amount such that themolar ratio of calcium to tartaric acid ranges from about 0.1:1 to 2.0:1with the ratio of moles of calcium to total moles of maleic and tartaricacid being less than 1; and (iii) a neutralizing agent comprising ahydroxide of a monovalent cation in an amount such that the ratio ofmoles of monovalent cation to moles of maleic acid plus moles oftartaric acid minus moles of calcium ranges from about 2.1:1 to 3.8:1.(b) maintaining said aqueous reaction mixture at a temperature of fromabout 20° C. to 120° C. for a time period sufficient to form a reactionproduct mixture of said 1-hydroxy-3-oxa-1,2,4,5-pentane tetracarboxylicacid salts and 3,6-dioxa-1,2,4,5,7,8-octane hexacarboxylic acid salts;(c) lowering the pH of reaction mixture of step (b) to the range of fromabout 4.5 to about 5.5 and cooling the mixture to precipitate calciumtartrate and monosodium maleate in two steps wherein the pH is firstreduced to a range of from about above 6 to about 9 and then loweringthe pH more rapidly than in said first step whereby unreacted startingacids are precipitated in particles of a size which provides increasedporosity and filter rate; (d) removing the precipitate from the reactionmixture formed in step (c), then reacting said precipitate with calciumcarbonate and sufficient maleic acide to convert the monosodium maleateto calcium maleate and employing said maleate in step (a); (e) treatingthe reaction mixture from step (d) with a carbonate or bicarbonatewhereby calcium carbonate precipitates; (f) removing the calciumcarbonate from the reaction mixture of step (e) and reacting saidcarbonate with maleic acid to form a calcium salt of maleic acid; (g)employing said calcium salt of maleic acid to prepare additional ethercarboxylates in step (a) above; and (h) recovering and purifying thereaction mixture from step (f).
 24. A process of claim 23 wherein thecarbonate is an alkali metal carbonate.
 25. A process of claim 24wherein the alkali metal is sodium.
 26. A process of claim 24 whereinthe bicarbonate is sodium bicarbonate.